The aim of this project is to determine the influence of specific structural features of the 5'-terminal portion of eukaryotic mRNA on initiation of protein synthesis in vitro. By comparing the ribosome-binding efficiencies of mRNA's containing different 5' ends the following conclusions have been reached: 5'-terminal m7G has a strong promoting influence on mRNA selection by eukaryotic ribosomes. The presence of the 2'-O methyl group as well as the nature of the penultimate residue also have a positive influence at this step, under mRNA excess conditions.